neuroscience requires us to reconsider this twofold classication of human behavior. First, there is an increasing number of psychological ndings indicating that a great
deal of our daily life is driven by automatic, unintended and unconscious mental processes, which involve little intention, attention, effort, control and awareness
Bargh, 1997, Bargh Chartrand, 1999; Kirsch Lynn, 1999. Automaticity penetrates into almost every aspect of our mental life, including perception, social
cognition, motor performance, the setting of behavior goals and motivations, and subjective evaluations and judgements. Many forms of automatic mental activities
develop out of repeated learning and experience from intentional, mindful, and effortful cognition and action. Second, intentional actions can also involve substan-
tive automatic elements. Once the critical situational context is encountered, people with specic prior intentions or simple plans on when, where, and how to act can
initiate intended actions immediately, efciently and effortlessly, which does not require conscious and deliberative control Gollwitzer, 1996, 1999. Third, there is
some neurobiological evidence showing that even in typical voluntary action the readiness potential to act takes place before the subjective experience of intention or
decision Libet, 1985, which means that voluntary actions can be initiated by unconscious brain processes instead of conscious intention or decision, as assumed
by folk psychology. These ndings suggest that the classical dichotomous framework for understanding human behaviors is too simple to describe human activities. The
voluntariness and deliberateness of human action are not all or none, but rather a matter of degree. Between the two ends of endogenously and intentionally initiated,
fully controlled human actions and simplest reexive behaviors, there is a wide range of activities of which a theory of action needs to make sense. Only within this
enlarged perspective can we appreciate the signicance of emotion in human action.
3. The hierarchy of the human motor system
Actions are usually embodied in voluntary bodily movement, under control of the motor system. The motor system is organized functionally as well as anatomically in
a hierarchy Gallistel, 1980; Gazzaniga et al., 1998; Ghez Krakauer, 2000 see Figure 1.
[T]he lowest level of this hierarchy is the spinal cord. Not only do spinal mechanisms provide a point of contact between the nervous system and
muscles, but also simple reexive movements can be controlled at this level. At the highest level are premotor and association areas. Processing
within these regions is critical for action planning based on present percep- tual information, past experience, and future goals. The motor cortex and
brainstem structures, with the assistance of the cerebellum and basal ganglia, translate an action into movement and coordinate the execution of
an action plan. Gazzaniga et al., 1998, p. 378
The brainstem contains most of the neural structures essential for rhythmic activities involving breathing, eating, eye movements, and facial expressions. In addition, the
F
IG
. 1. The motor hierarchy adapted from Gazzaniga et al., 1998, p. 378.
brainstem also projects to the spinal cord. It is a primary source of control over spinal activity.
The anatomical hierarchy of the motor system supports the functional hierarchy of action organization. Abstract action intentions or plans are formed on the highest
levels, transformed into motor programs at intermediate levels, and then imple- mented at the lowest levels of the hierarchy. Endogenous voluntary movement
originates in the cortex Krakauer Ghez, 2000. The intentions, plans, or goals of action need not be concerned with the details of a bodily movement. Lower levels
of mechanisms are needed to translate and realize motor commands into muscular movements. The premotor and supplementary motor areas are important for plan-
ning and coordinating complex and novel sequences of movement. They are in turn inuenced heavily by the prefrontal cortex, which is believed to be involved in
higher-level planning, attention, working memory, decision-making, and emotional feelings. The primary motor cortex controls relatively simple and routine features of
movement. The cerebellum and the basal ganglia provide feedback circuits that regulate cortical motor areas and the brainstem. They are necessary for smooth and
accurate movement and posture.
The cerebral cortex can regulate the activity of spinal neurons in direct and indirect ways Schieber, 1999. Direct connections are provided by the cortico-
spinal tract, the descending pathway that originates from the cortex and terminates directly on the spinal cord. The cortico-spinal tract, one of the latest evolutionary
adaptations appearing only in mammals, especially humans, has a major signicant role in the execution of voluntary movement Porter Lemon, 1993. Indirect
pathways from the cerebral cortex to the spinal cord involve centers in the brain- stem. While the direct pathway has more control on distal limb muscles in behaviors
such as manipulation of small items, indirect pathways heavily inuence proximal muscles during behaviors such as ambulation. The existence of two different
pathways for voluntary control in the human motor system introduces both exibility and complexity into human action.
4. The amygdala: a center for emotional information processing
